1. Field of Invention
The present invention relates to a method for measuring a silicon trench depth. More particularly, the present invention relates to a method for measuring the silicon trench depth using optics.
2. Description of Related Art
Depth measurement in a semiconductor process involving probing the substrate surface. Since the depth of a trench or an opening is measured according to the surface fluctuation of the substrate, the method is typically a contact-type measurement. If the surroundings interfere with a test probe during depth detection, the resulting measurements may be inaccurate, so a stress is usually applied to the test probe to prevent the probe from drifting. This adds a loading to the probe so as to allow easy measurement. However, such stress causes damage, as well as cuts, on the substrate surface. Furthermore, the stress leads to electrical problems such as bridging or leakage current. As a result, the reliability of the device is reduced.
As the size of the probe is not reduced without limitation, the probe is easily stuck in the trench during measurement when a very narrow trench, such as the trench with an opening width of the below 1 xcexcm, is measured. Since the probe has a lower measurement rate, it is unable to perform a great deal of tests. In addition, there may be errors for the measurement accuracy, which reduces the resolution when the substrate is less smooth.
The invention provides an optical method for measuring a trench depth, where a non-destructive measurement is performed on a substrate to improve the reliability of a device.
It is therefore an object of the invention to provide an optical method, which method allows measurement of a narrower trench and provides a higher measuring rate, so that operation time is saved while resolution is improved.
As embodied and broadly described herein, the invention provides an optical method for measuring the trench depth, applicable to a substrate having a trench, wherein the substrate has a first surface, and the trench has a bottom surface to serve as a second surface as well as a depth. The method involves measuring a total reflectance (R) from the substrate using different wavelengths, wherein R is determined by a first actual reflectance from the first surface, a second actual reflectance from the second surface, and a scattering factor (xcex94R). The second actual reflectance is then determined from the measurement of the first actual reflectance from the first surface and the calculation result of xcex94R. Since a trench depth d is determined from the second actual reflectance, d is calculated after acquiring the second actual reflectance.
The first actual reflectance in this case is determined from a first reflectance R1 and a first area factor xcex1, whereas the second actual reflectance is determined from a second reflectance R2 and a second area factor xcex2.
According to the present invention, the optical method for measuring the trench depth not only allows measurement of the narrower trench, but also provides a higher measuring rate. Furthermore, since the optical method provides non-destructive measurement, the reliability of the device increases.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further, explanation of the invention as claimed.